netdev - RE: [Intel-wired-lan] [PATCH bpf-next 2/6] samples/bpf: increment Tx stats at sending

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Message-ID: <5fa9aae46c442_8c0e208b5@john-XPS-13-9370.notmuch>
Date:   Mon, 09 Nov 2020 12:47:32 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Magnus Karlsson <magnus.karlsson@...il.com>,
        magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org,
        jonathan.lemon@...il.com
Cc:     maciejromanfijalkowski@...il.com, intel-wired-lan@...ts.osuosl.org,
        bpf@...r.kernel.org
Subject: RE: [Intel-wired-lan] [PATCH bpf-next 2/6] samples/bpf: increment Tx
 stats at sending

Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@...el.com>
> 
> Increment the statistics over how many Tx packets have been sent at
> the time of sending instead of at the time of completion. This as a
> completion event means that the buffer has been sent AND returned to
> user space. The packet always gets sent shortly after sendto() is
> called. The kernel might, for performance reasons, decide to not
> return every single buffer to user space immediately after sending,
> for example, only after a batch of packets have been
> transmitted. Incrementing the number of packets sent at completion,
> will in that case be confusing as if you send a single packet, the
> counter might show zero for a while even though the packet has been
> transmitted.
> 
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---

LGTM. Just one question then if we wanted to know the old value, packet
completion counter it looks like (tx_npkts - outstanding_tx) would give
that value?

Acked-by: John Fastabend <john.fastabend@...il.com>